feat: delete entry from the picker without closing telescope (#828)

This action is not mapped but you can do it yourself in your telescope setup call
Example config:
```lua
require("telescope").setup {
  pickers = {
    buffers = {
      mappings = {
        i = {
          ["<c-d>"] = "delete_buffer",
        }
      }
    }
  }
}
```

doc/telescope.txt

@@ -369,6 +369,15 @@ actions.open_loclist()                                *actions.open_loclist()*
 
 
 
+actions.delete_buffer({prompt_bufnr})                *actions.delete_buffer()*
+    Delete the selected buffer or all the buffers selected using multi
+    selection.
+
+
+    Parameters: ~
+        {prompt_bufnr} (number)  The prompt bufnr
+
+
 
 ================================================================================
                                                              *telescope.builtin*